The present invention relates to a thermal head driving/control apparatus which corrects printing density distortions occurring in a recording device which employs a thermal head. In many such recording devices, commonly found in facsimile equipment, picture information is recorded by a thermal head according to a linearly successive recording system. That is, an image is broken into a series of lines and is recorded one line at a time.
In such devices, the thermal head includes a plurality of heating elements formed on a substrate. The temperature of each heating element and the temperature of the substrate portion in the vicinity of a particular heating element are affected by the driving history of the heating element in recording previous lines. For example, if one heating element is driven to continuously generate heat for several contiguous lines, thermal energy will locally accumulate around that element, thereby increasing the temperature of the substrate portion located in the vicinity of the heating element. The resultant accumulated energy imposes a higher temperature on the heating element than that which would be imposed had the heating element not been driven continuously. Thus, the local temperature deviation of the heating elements and substrate affects the operating temperatures of the elements as successive lines are recorded. This deviation from operating temperatures normally expected for recording an image, if uncorrected, results in uneven printing density.
As a countermeasure, a method has been proposed in which the substrate is heated by a controlled heater. However, according to this method, it is necessary to detect the temperature of the substrate at several portions thereof before applying the correction. Accordingly, problems occur with this method in that (1) thermal response is poor, and (2) fine control for heating each individual element cannot be performed. It is an object of the present invention to overcome these problems.